The spine can be considered to be a series of movable segments made up of vertebrae and discs. Due to trauma, disease, and/or aging, the spine may be subject to degeneration. This degeneration may destabilize the spine and cause pain and/or nerve damage. Medical procedures are often required to either ease back pain, repair damage, or to prevent future damage.
One procedure that is often used to treat back pain or spinal damage is spinal fusion. Spinal fusion is a surgical technique used to combine (or fuse) two or more adjacent vertebrae. Supplemental bone tissue is used in conjunction with the patient's natural osteoblastic processes in a spinal fusion procedure. Spinal fusion is used primarily to eliminate back pain caused by the motion of the damaged vertebrae by immobilizing adjacent vertebrae, reestablishing normal spinal column height and lordosis, and relieving pressure on spinal nerve roots. Conditions for which spinal fusion might be done include degenerative disc disease, treatment of a spinal tumor, a vertebral fracture, scoliosis, herniation of the disc, spondylolisthesis, or any other condition that causes instability of the spine.
As a part of the procedure, bone or bone substitute grafts are commonly placed between the vertebrae following excision of a damaged spinal disc, and topically along the posterolateral portion of the spine, adjacent to the pathologic segment. This helps induce bone growth between two adjacent vertebrae and fuses the facets in the posterior spinal segments. Currently available synthetic bone grafts, however, are typically not optimal and natural autologous bone grafts are in limited in supply, while cadaveric or allograft bone grafts carry a risk of disease transmission. These grafts often collapse and/or resorb too quickly, even in the presence of supplemental proteins such as bone morphogenic protein (BMP), to encourage sufficient bone growth or good quality, healthy bone formation.
While there are a number of products on the market that are in the category called “bone void fillers”, most if not all of them are cleared for use as a standalone implant. However, there are specific situations in supporting the formation of an arthrodesis (bony fusion) that require an approach that is more malleable and shape retaining than granular or putty forms of bone void fillers.
There is therefore a need for a bone graft device that adequately promotes spinal fusion to treat degenerative disc disease and other spinal conditions, while providing improvements over the prior methods. The disclosed invention embodies the combination of an allograft material (i.e., cadaveric-derived bone chips or other bony forms) with a synthetic material which contains hydroxyapatite and gelatin in close proximity and further contained in a pouch or bag that is permeable, which serves to hold the materials contained therein in place at the site of bony pathology while remaining malleable during implantation. Graft migration, which can be a problem with current approaches using granular bone void fillers, is eliminated, ensuring that the graft material will be resident at the site of repair. Additionally, there is a need for bone graft devices that can be attached to implanatable instrumentation and introduced to an area of bone during surgery and additionally do not migrate during surgery.